The Effects of Photobioreactor Type on Biomass and Lipid Production of the Green Microalga Monoraphidium pusillum in Laboratory Scale

Abstract

Mass production of microorganisms, algae among them, for new bioactive compounds and renewable innovative products is a current issue in biotechnology. The greatest challenge of basic research on this topic is to find the best solution for both physiology and scalability. In this study, the main goal was to highlight the contradictions of physiological and technological optimization in the same, relatively small, laboratory scale. The green alga Monoraphidium pusillum (Printz) Komárková-Legnorová was cultured in a conventional Erlenmeyer flask (as air bubbled in a tank-type photobioreactor) and in a hybrid (fermenter type + helical tubular type) photobioreactor of the same volume (2.8 L). Higher cell numbers from 1.7–2.3-fold, 2–2.8-fold higher dry masses, and 1.9–2.6-fold higher total lipid contents (mg·L−1) were measured in the tank reactor than in the hybrid reactor. Cultures in the conventional tank reactor were characterized with better nutrient utilization (42.8–77.7% higher phosphate uptake) and more diverse lipid composition than in the hybrid reactor. The study highlights that well-scalable arrangements and settings could be not optimal (or unsuitable in some cases) from a physiological point of view. The results suggest certain developmental directions for complex, well-scalable devices and highlight the importance of testing the gained physiological optima on these systems.

Laboratory- and Pilot-Scale Cultivation of Tetraselmis striata to Produce Valuable Metabolic Compounds

“…The most critical aspects of microalgae cultivation systems are light utilization and distribution, as well as proper mixing in all parts of the PBR [ 7 , 43 ]. Light is the most important factor as it determines growth, specific growth rate and biomass chemical composition by influencing photosynthesis rate [ 26 , 44 ].…”

“…Proper mixing ensures uniformity, guarantees that all cells are equally exposed to light, and prevents cell sedimentation and cell attachment to the walls of the PBR [ 15 ]. Therefore, different types of PBRs with different mixing strategies (to maximize light penetration) have been the subject of many studies [ 7 , 16 , 43 ]. In addition, medium formulation, namely the type, source, and nutrient concentration can also significantly affect biomass production.…”

“…For example, microalgae can be cultivated in simple and low-cost aquarium tanks, which are usually illuminated from the top. Aquariums are among the less common PBRs used for microalgae cultivation and scaling up may be challenging due to light-driven issues [ 43 ]. Thus, further research is required on the use of aquarium tanks.…”